AB to Step 7 CPU selection

Mike_RH

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Join Date
Sep 2006
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Toronto
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Does anyone have any rules of thumb or guidelines for selecting a S7 CPU, when converting an application from AB?

The IO count is straightforward, but how to compare the memory size of the processors?

I'm looking at CompactLogix, SLC or PLC-5 to S7.

All comments appreciated.
 
Hi Mike.

For PLC5 or SLC500 to S7, then they have almost the same memory footprint for the same code. Maybe S7 uses a little more memory than PLC5 and SLC500 for the same code. Then again, in S7 you can write reusable code that save on code memory. So overall, approximately the same. In the latest generation S7 all CPUs are more performant than PLC5/SLC500. And if you go for 315-2PN/DP or better, you have more than enough memory.

For CompactLogix, I have not enough experience.
A CompactLogix uses many times the same memory as PLC5/SLC500, I have heard 5 times and 10 times as much. On the other hand, CompactLogix has much more memory than PLC5/SLC500. Someone who knows better than me can fill in the details.
 
I'm looking for the compactlogix answer too :)

i heard also that new 300 are huge and fast as the last 317 but...i don't remember if it concern only 315 or 314 also ?

Our Siemens engeener told me about comparing the same project made with 3 separate controllogix inside only 1 317 and the 317 got a faster scan time than the 3 controllogix but i don't have the detail about the AB model...And there is still S7-400 availaible to go 1 step further

On my personal side, i can't tell because i never did any application to overload a 2000+ 314/315 memory capacity at this time....

I usually build around 315 pn/dp most of the time with slaves s7-200 and a DP module. MAster/slave made with Profibus and Ethernet availaible for any availaible Scada connection.....
I'm looking to switch to S7-1200 over Profinet but i wait to get a combined software doing both plc...
 
Thanks for the answers guys.
Jesper, you've confirmed my gut for the SLC and PLC-5.
But I would like to hear from anyone who has done the same machine with CompactLogix and a S7 solution to hear their thoughts.
Bueller? Bueller?
 

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